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Easy Shaft Alignment


Successful alignment of rotating machinery depends significantly on how much emphasis is put on the alignment preparation and planning stages. Proper machinery alignment reduces the chance of an equipment failure, helping end users avoid unnecessary downtime and excessive maintenance time and costs. Preparing thoroughly and choosing an appropriate alignment method can help ensure a smooth process.


Choose an Alignment Method

After preparing for alignment, end users must choose an alignment method appropriate for their machinery. Many alignment methods require brackets and arms for mounting the measuring equipment. As the length of the arms increases, the arms become more susceptible to sagging, which can cause significant measuring errors if end users do not take the sagging into account. Figure 1 illustrates the typical method to check for sagging arms. End users should add the values they record to the readings they take during alignment. The major methods for checking alignment are discussed in this section.


Method 1 - Face and Periphery

The face and periphery method is the oldest and most widely used dial indicator method. Figure 2 illustrates the correct setup for this method, which is good for large-diameter hubs with a short distance between shaft ends.

Advantages:

  • The end user only needs to rotate one shaft.
  • Visualizing shaft positions is easier compared to other methods.

 

Disadvantages:

  • It is difficult to obtain face readings if there is any axial float.
  • An end user typically has to remove the coupling.
  • It is more complicated to make the graphical calculations compared with other methods.
  • Any out-of-roundness in the hub periphery or out-of-squareness in the hub face—meaning the hub flange is not round or flat and square relative to the shaft—will affect the readings.

Method 2 - Reverse Periphery (Indicator) Method

The reverse periphery (indicator) method is becoming increasingly popular and is the optimal method for most alignments. Figure 3 illustrates the correct setup for this method.

Advantages:

  • It is generally more accurate than the face and periphery methods.
  • Axial float, or out-of-roundness or out-of-squareness in the hub, does not affect the readings.
  • It is easier to plot graphically compared with other methods.
  • It is possible to make measurements with the coupling in place.

Disadvantages:

  • End users must rotate both shafts.
  • It is not accurate for close-coupled shafts.

Method 3 - The Laser System

The modern laser system (see Figure 4) consists of either two laser/detector units or one laser and one mirror/prism reflector unit. One unit is attached to each shaft, and the laser/detectors are connected to a keyboard/display unit by a cable or via a wireless Bluetooth system. The system operates using the principles of reverse periphery, detecting the movement of the laser beams as a measure of the misalignment.

Advantages:

  • The system fits a variety of shafts.
  • End users do not have to remove the coupling.
  • End users can measure long spans with no sagging issues.
  • It is not affected by axial float.
  • The system detects the soft foot condition easily.

 

Disadvantages:

  • The system is not suitable for couplings with backlash.
  • Heat or steam can affect its accuracy.
  • The system is expensive.
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